Tobacco use continues to be a major public health problem in the United States, with one-third of users becoming dependent, and tobacco smoking is the leading avoidable cause of death in the United States. In the United States alone, exposure to tobacco smoke by nonsmokers (second-hand smoke exposure) is believed to cause an additional 50,000 deaths from heart disease and cancer, 1 million lung and ear infections, and increased asthma episodes in an additional 1 million children. The rapid growth of electronic cigarette use may have dramatic consequences on the population. The electronic cigarette industry generated over $1 billion in revenue in the United States last year and is predicted to pass traditional cigarette sales by 2047. Moreover, the danger of electronic cigarette is that they are marketed as safe to use, but virtually no research has been conducted on the consequences of nicotine vapor exposure on the brain and development of nicotine dependence. Second-hand smoke and electronic cigarette use lead to clinically significant blood nicotine levels. We hypothesize that they will produce important neuroadaptations that contribute to increased risk of developing dependence and facilitating relapse. The present proposal focuses on animal studies to investigate the specific effects of inhalation of nicotine at levels similar to electronic cigarettes on the development of nicotine dependence and relapse. The first hypothesis is that chronic exposure to nicotine vapor at concentrations similar to electronic cigarettes, or even lower, will affect key behaviors related to nicotine dependence (anxiety-like behavior, hyperalgesia). The second hypothesis is that chronic exposure to nicotine vapor at concentrations similar to electronic cigarettes, or even lower, will increase the escalation of nicotine intake and provoke relapse after a period of abstinence. To determine the exact effect of nicotine inhalation, we developed an innovative inhalation system to expose rats to known concentrations of nicotine in the air. The use of this new animal model of nicotine inhalation will provide a unique opportunity to determine the lowest level of nicotine exposure that is required to produce behavioral changes that may facilitate the acquisition of and relapse to nicotine dependence. The results of these studies will provide (i) the lowest dose of nicotine vapor required to increase the risk for nicotine dependence, (ii) evidence of whether electronic cigarette use is associated with increased risk of the acquisition of and relapse to nicotine dependence, and (iii) important information for nicotine dependence prevention efforts and policymakers.